I am not so sure about this. You can't get social security benefit if you are not a US citizen or green card holder even though you have paid all the payroll taxes.
We have to do things legally even the law is inconvenient to you. I think a quite few people are taking advantage of the situation that US government and Chinese government not communicating with each other and don't know you are getting both retirement benefits (this is also true by not reporting investment income such as interest in Chinese bank, real estate transaction income etc). However, this doesn't make it right or legal!!!